The present invention relates to an automatic wheel alignment measurement system. In particular, the invention relates to a hand held wheel alignment system.
Proper alignment of the wheels of an automotive vehicle is important for both proper handling of the vehicle, as well as proper tire wear. The wheel alignment parameters which are measured and adjusted in order to achieve proper wheel alignment are camber, caster, steering axis inclination (SAI) and toe angle.
Camber is defined as the angle which the wheel makes with respect to a vertical plane when looking at the wheel from either the front or rear of the automobile. Any wheel of an automobile can have camber.
Caster is angle which the steering axis of a steerable wheel (typically one of the front wheels) makes with respect to a vertical plane which perpendicular to the longitudinal direction of the automobile.
Steering axis inclination (SAI) is the inclination of the steering axis with respect to a vertical plane which is parallel to the longitudinal direction of the automobile.
Toe was originally defined as the difference in the distance between the front edges of two opposite wheels and the distance between the rear edges of the same two wheels. Toe can also be defined in terms of a angular relationship of the plane of a wheel (perpendicular to its turning axis) relative to a predetermined longitudinal vehicle axis. When the forwardmost portions of a pair of adjacent wheels are closer together than the rear portions of those wheels, they are commonly referred to as in a "toe-in" condition. When the rear portions of wheels are closer together than the front portions, the condition is commonly referred to as "toe-out."
Camber is a tire wearing angle and also affects handling of the automobile Caster and SAI do not affect tire wear but are important for directional control. Toe is a tire wearing angle and also affects the position of the steering wheel required to maintain travel of the automobile along a straight line.
Caster, Camber, and SAI are typically measured using head units coupled to the wheels of an automobile and attached to a hand held module. For example, U.S. Pat. No. 4,594,789 by Marino et al describes an automatic wheel alignment system and is incorporated herein by reference.
Prior art automatic wheel alignment systems typically require a console which is set apart from the automobile. This console typically weighs several hundred pounds and stands four to six feet high and two to four feet wide. Often, it is difficult for an operator to view the console while simultaneously adjusting camber, caster, SAI, and toe of the wheel.
There is a continuing need for an automatic wheel alignment system which is convenient to use and provides an improved user interface.